1. Field of the Invention
The present invention relates to a hydraulic braking pressure generating apparatus for vehicles, and more particularly, the hydraulic braking pressure generating apparatus provided with a barking stroke simulator.
2. Description of the Related Arts
Heretofore, there are known various hydraulic braking pressure generating apparatuses for vehicles, which are provided with braking stroke simulators. Among them, such an apparatus as discussed below has been disclosed in Japanese Patent Laid-open publication No. 11-59349. According to this publication, may be derived such an apparatus as constituted by a first piston which is moved back and forth in response to operation of a brake pedal, an elastic member which provides a stroke of the first piston in response to braking operation force of the brake pedal, and a second piston which is slidably accommodated in a cylinder housing to define a master pressure chamber in front of the second piston, and define a simulator chamber behind the second piston and in front of the first piston, and which is moved back and forth in response to the braking operation force of the brake pedal transmitted to the second piston through the first piston and the elastic member. And, a changeover device may be provided for selectively changing a communicating state for communicating the simulator chamber with an atmospheric pressure reservoir, and a cut-off state for blocking the communication between the simulator chamber and the atmospheric pressure reservoir.
In general, the stroke simulator is adapted to provide the brake pedal with a stroke in response to the braking operation force, when a pressure control device is normal, i.e., when the communication between the master cylinder and the wheel brake cylinder has been blocked. And, according to the hydraulic brake apparatus as disclosed in the Japanese Patent Laid-open publication No. 11-59349, the stroke simulator is disposed between the brake pedal and a master piston. In view of the fact that it is required to provide a large stroke of the brake pedal in response to a stroke of the stroke simulator, when the pressure control device is failed, i.e., when the hydraulic pressure is supplied from the master cylinder to the wheel brake cylinder, there is provided a cut-off device for blocking the communication between the simulator chamber and the atmospheric pressure resevoir in response to movement of the master piston.
In Japanese Patent Laid-open publication (PCT) 2001-526150, which corresponds to the U.S. Pat. No. 6,192,685 B1, may be derived such an apparatus as constituted by a first piston which is slidably accommodated in a cylinder housing, and moved back and forth in response to operation of a brake pedal, a second piston which is slidably accommodated in the cylinder housing to define a simulator chamber in front of the second piston, and which is moved back and forth in response to the braking operation force of the brake pedal transmitted to the second piston through the first piston and hydraulic pressure in the simulator chamber, and an elastic member which provides a stroke of the second piston in response to the braking operation force of the brake pedal. And, a changeover device may be provided for selectively changing a communicating state for communicating the simulator chamber with an atmospheric pressure reservoir, and a cut-off state for blocking the communication between the simulator chamber and the atmospheric pressure reservoir.
Furthermore, according to the Japanese Patent Laid-open publication (PCT) 2001-526150, may be derived an absorbing member which absorbs brake fluid of the amount determined in response to the hydraulic pressure discharged from the simulator chamber, and which provides a stroke of the second piston in response to braking operation force of the brake pedal. And, a changeover device may be provided for selectively providing an operative state of the absorbing member and an inoperative state of the absorbing member.
With respect to a general hydraulic brake apparatus, in order to remove air introduced into the brake fluid in a hydraulic braking circuit, a so-called air-bleeding operation is performed. According to the apparatuses as described above, however, when the air-bleeding operation is performed after it was installed on a vehicle, even if the changeover device was actuated, the stroke of the stroke simulator could not be prevented from being stroked, due to insufficiency of brake fluid to be filled, whereby both of the stroke simulator and the master piston would stroke simultaneously. Therefore, it is required to provide an appropriate distance for the sum of a maximal stroke of the stroke simulator and a maximal stroke of the master piston, so as to prevent the brake pedal from being interfered with a vehicle floor or the like. In order to meet this requirement, however, if the maximal stroke of the stroke simulator was set to be capable of obtaining a proper brake feeling when the pressure control device disposed in the hydraulic pressure circuit was normal. Therefore, if the pressure control device was failed, it would be a limit to be constituted that the maximal stroke of the master piston could supply only a minimal amount of brake fluid required for stopping the vehicle, into the wheel brake cylinder. In view of a reliability of the apparatus, therefore, an improvement to it has been required.